The present invention disclosed herein relates to a carrier head of a chemical-mechanical polishing apparatus, and more particularly, to a membrane assembly and a carrier having the membrane assembly, which can enlarge an active area of a wafer by pressurizing an edge portion of the wafer.
A chemical-mechanical polishing (CMP) apparatus is used for widely flattening the surface of a wafer by eliminating a height difference between a cell region and a peripheral circuit region, which is caused by an uneven wafer surface that is created by repeatedly performing a masking process, an etching process and a wiring process. Also, the CMP apparatus is used for precisely polishing the wafer surface to improve a wafer surface roughness caused by separating a contact/wiring layer for forming a circuit and highly integrating a device.
In the CMP apparatus, a carrier head holds or receives a wafer by directly and indirectly vacuum-suctioning the wafer while a polishing surface of the wafer is facing a polishing pad during a polishing process. Generally, a membrane type of carrier head is being widely used. Also, there has been proposed a multiple-region division polishing carrier head technology in which a polishing profile of the wafer can be variously controlled by locally applying different pressures on the surface of the wafer. This technology is a more advanced technology than a technology in which the surface of the wafer is uniformly polished by simply applying a uniform pressure on the surface of the wafer.
FIGS. 1A and 1B are schematic views illustrating the structure of a typical multiple-region division polishing membrane type of carrier head H and the operation state thereof when certain air pressures P1 and P2 are loaded into divided chambers C1 and C2, respectively.
As shown in FIG. 1A, a membrane 110 is installed on a bottom surface of a carrier head H. A ring-shaped membrane supporting stem 120 is integrally formed on a top surface of the membrane 110. The membrane 110 is divided into inner and outer chambers C1 and C2 by the ring-shaped membrane supporting stem 120. The membrane 110 is fixed by a membrane plate 11 and a membrane clamp 12 that are stacked inside the upper portion of the membrane 11, and a retainer ring 3 surrounding the outer circumferences of the membrane plate 11 and membrane clamp 12.
In the above-described carrier head H, when predetermined air pressures P1 and P2 are loaded through central and outer air passages 2 and 24, respectively, as shown in FIG. 1B, the air pressure P1 applies a predetermined pressure to the inner chamber C1 to allow the inner chamber C1 to expand. In addition, the air pressure P2 applies a predetermined pressure to the outer chamber C2 to allow the outer chamber C2 to expand. At this point, since an upper end of the membrane supporting stem 120 is fixed by the membrane plate 11 and the membrane clamp 12, it is not deformed by the expansion of the inner and outer chambers C1 and C2. Accordingly, a sharp circular inflexion point 121 is formed between the inner and outer chambers C1 and C2 along an outer circumference of a lower end of the membrane supporting stem 120.
The inflection point 121 has a bad influence upon performing a multiple polishing process, which is performed by a locally differential pressure load to realize a predetermined region division profile on a surface of a single wafer. That is, since a rear surface of the wafer is unstably pressurized under a sharp shape/pressure variation at a portion of the inflection point 121, the polishing speed at the region division boundary is lowered and thus an abnormal polishing phenomenon occurs. As a result, the production yield of semiconductors is reduced.
In case of the above-described typical carrier head, a wafer is adsorbed on the bottom surface of the membrane coupled to the bottom surface of the carrier head. In this case, in order to fix the wafer, an indirect suctioning method is used. For the indirect suctioning method, since a chamber vacuum pressure delivered to the wafer is relatively less than a pressure delivered to the membrane, the wafer suctioning error may occur. Thus, the wafer may be separated from the carrier head and thus damaged in the course of delivering the wafer or mounting/dismounting the wafer.
Particularly, in case of a typical carrier head membrane, since the pressure cannot be uniformly applied to the wafer adsorbed on the bottom surface of the membrane and thus the edge region of the wafer is not sufficiently polished. As a result, the whole region of the wafer including the edge region cannot be used to produce the semiconductor device, resulting in deterioration of the yield.
Meanwhile, the membranes are relatively expensive components in the carrier head but they are expendables that are partly damaged during the polishing process or cannot be used anymore after they are used for a long time. Therefore, the membranes have to be periodically replaced. However, since the membrane has a complicated structure having the fixing portion for coupling to the membrane clamp and the partition for the multiple region division polishing, the replacement of the membrane requires the assembling and disassembling of components of the carrier head. This deteriorates a life span of the carrier head and efficiency of the polishing process.
Therefore, there is a need for a membrane that can be easily replaceable with a new membrane and does not damage components of the carrier head in the course of replacing the membrane.